Hardening of flexible trailing arms

Abstract

The invention relates to a method for manufacturing of a flexible trailing arm for a wheel axle suspension of a vehicle such as a lorry or a trailer. In the method a steel blank is heated. Next, the blank is formed into the desired shape of the trailing arm by means of a suitable forming process. Following that the trailing arm is austempered by cooling it in a warm fluid medium.

The invention claimed is: 
     
       1. A flexible trailing arm for a wheel axle suspension of a vehicle, wherein the flexible trailing arm comprises steel with a bainitic structure which has a tensile strength of approximately 1300-1600 N/mm 2 ;
 wherein the trailing arm has exterior regions which extend from an outer surface to a certain depth, which exterior regions have a bainitic structure; and 
 wherein the trailing arm has interior regions, located more to the interior than the exterior regions, which have another structure than bainitic structure. 
 
     
     
       2. The flexible trailing arm according to  claim 1 , wherein said structure of the interior regions have a pearlite structure. 
     
     
       3. The flexible trailing arm according to  claim 1 , wherein said structure of the interior regions have a ferrite structure. 
     
     
       4. The flexible trailing arm according to  claim 1 , wherein said structure of the interior regions have a mixture of pearlite and ferrite structures. 
     
     
       5. The flexible trailing arm according to  claim 1 , wherein the trailing arm is a forged part. 
     
     
       6. The flexible trailing arm according to  claim 1 , wherein the trailing arm comprises a spring portion, a hinge eyelet on a front end of the spring portion, and a curved portion on a rear end of the spring portion, which curved portion has a concave contact surface. 
     
     
       7. The flexible trailing arm according to  claim 6 , wherein the spring portion of the arm has a substantially rectangular cross section having a width and a thickness, the width being greater than the thickness. 
     
     
       8. A flexible trailing arm for a wheel axle suspension of a vehicle comprising a spring portion, a hinge eyelet on a front end of the spring portion, and a curved portion on a rear end of the spring portion, which curved portion has a concave contact surface, wherein the spring portion of the arm has a substantially rectangular cross section having a width and a thickness, the width being greater than the thickness, the flexible trailing arm comprising steel with a bainitic structure, wherein the trailing arm has exterior regions which extend from the outer surface to a certain depth, which exterior regions have said bainitic structure, and wherein the trailing arm has interior regions, located more to the interior than the exterior regions, which have another structure than bainitic structure. 
     
     
       9. The flexible trailing arm according to  claim 8 , wherein said structure of the interior regions have a pearlite structure. 
     
     
       10. The flexible trailing arm according to  claim 8 , wherein said structure of the interior regions have a ferrite structure. 
     
     
       11. The flexible trailing arm according to  claim 8 , wherein said structure of the interior regions have a mixture of pearlite and ferrite structures. 
     
     
       12. A wheel axle suspension for a trailer comprising a flexible trailing arm for a wheel axle suspension of a vehicle comprising a spring portion, a hinge eyelet on a front end of the spring portion, and a curved portion on a rear end of the spring portion, which curved portion has a concave contact surface, wherein the spring portion of the arm has a substantially rectangular cross section having a width and a thickness, the width being greater than the thickness, the flexible trailing arm comprising steel with a bainitic structure, wherein the trailing arm has exterior regions which extend from the outer surface to a certain depth, which exterior regions have said bainitic structure, and wherein the trailing arm has interior regions, located more to the interior than the exterior regions, which have another structure than bainitic structure. 
     
     
       13. A trailer comprising a wheel axle suspension according to  claim 12 . 
     
     
       14. A flexible trailing arm for a wheel axle suspension of a vehicle, wherein the flexible trailing arm comprises steel with a bainitic structure, wherein the trailing arm has exterior regions which extend from an outer surface to a certain depth, which exterior regions have a bainitic structure, and wherein the trailing arm has interior regions, located more to the interior than the exterior regions, which have another structure than the bainitic structure. 
     
     
       15. The flexible trailing arm according to  claim 14 , wherein said structure of the interior regions have a pearlite structure. 
     
     
       16. The flexible trailing arm according to  claim 14 , wherein said structure of the interior regions have a ferrite structure. 
     
     
       17. The flexible trailing arm according to  claim 14 , wherein said structure of the interior regions have a mixture of pearlite and ferrite structures.